The field of the invention is fluid catalytic cracking (FCC).
FCC technology, now more than 50 years old, has undergone continuous improvement and remains the predominant source of gasoline production in many refineries. This gasoline, as well as lighter products, is formed as the result of cracking heavier, less valuable hydrocarbon feed stocks such as gas oil.
In its most general form, the FCC process comprises a reactor that is closely coupled with a regenerator, followed by downstream hydrocarbon product separation. Hydrocarbon feed contacts catalyst in the reactor to crack the hydrocarbons down to smaller molecular weight products. During this process, coke tends to accumulate on the catalyst which is burned off in the regenerator.
It has been recognized that due to environmental concerns and newly enacted rules and regulations, saleable petroleum products must meet lower and lower limits on contaminates, such as sulfur and nitrogen. New regulations require essentially complete removal of sulfur from liquid hydrocarbons that are used in transportation fuels, such as gasoline and diesel.
The least valuable product from an FCC process is slurry oil which is withdrawn from the bottom of the FCC main fractionation column and burned as fuel. The slurry oil comprises the heaviest product mixed with catalyst particles that have not been successfully removed from the FCC products. LCO is also produced in an FCC unit and can be directed to the diesel pool. However, LCO may degrade the quality of the diesel pool due to its high aromaticity and low cetane value. The slurry oil is less valuable than LCO. Due to operational constraints of the FCC main fractionation column, the slurry oil leaves the main fractionator with an appreciable amount of hydrocarbons in the boiling range of LCO and a small amount in the boiling range of gasoline. Heavy cycle oil (HCO) is an FCC liquid stream pumped around to cool the main fractionation column but is not often recovered from the main fractionation column.
Hydroprocessing is a process that contacts a selected feedstock and hydrogen-containing gas with suitable catalyst(s) in a reaction vessel under conditions of elevated temperature and pressure. Hydrotreating is a hydroprocessing process in which heteroatoms such as sulfur and nitrogen are removed from hydrocarbon streams to meet fuel specifications and to saturate olefinic and aromatic compounds. Hydroprocessing is also used to prepare fresh hydrocarbon feed for FCC processing by demetallizing the FCC feed. Metals, vanadium and nickel, in the FCC feed can deactivate the FCC catalyst during the FCC process.
The demand for diesel has increased over gasoline in recent years. Increased recovery of LCO produced in an FCC unit can be directed to the diesel pool and augment diesel production. Further conversion of the HCO to LCO and other motor fuel products would also be desirable.